Mirror one domain to two servers?

[Andy lague]

At 06:24 AM 11/20/96 GMT, Cricket Liu wrote:

>Cisco's LocalDirector product, from what little I know about it, might
>help address this. It can return a list of IP addresses with the
>entries sorted according to some notion of "load" on the target, which
>one would hope also accounts for the target being down.
>

LocalDirector actually works a little differently. DNS would return a
single address for www.xyz.com, which would be the LocalDirector address.
LocalDirector then dynamically load balances connections between multiple
local servers based on response times. This allows for the load to be
shared evenly among multiple servers with different performance
characteristics. Also, if a server goes down, its response time goes to
infinity and connections are not sent to it. The fact that there are
multiple servers behind LocalDirector is completely transparent to the user.

[Dan Brown]

>
>On Tue, 12 Nov 1996 08:23:23 -0500, me...@goldstag.com* (Melvin C.
>Etheridge) wrote:
>>How can I mirror www.xyz.com to two servers?
>>
>>Say if one server goes down the other one will answer back.
>
>Unfortunately, that's not really possible with a vanilla version of
>BIND. You could give BIND two addresses for www.xyz.com, I belonging
>to each real server, and BIND will alternately give out the first
>server's IP address first, and then the second server's IP address
>first. That'll spread the load between the two, but if one fails,
>roughly half of the queries to www.xyz.com will also fail.

This is actually a failing with the client, not the server end of things.
Some programs, like some versions of telnet, will try multiple address for
a host, in succession till it gets a connection. Its one of those "should"
do things not a "must" do thing per RFC 1123, I believe.

It is something that browsers _could_ fix if they wanted to, but requires
re-writing network code.

later.
Dan
--
Dan Brown
dbr...@seismo.css.gov

[m...@f5.com]

On Wed, 20 Nov 1996, Cricket Liu wrote:

> On Tue, 12 Nov 1996 08:23:23 -0500, me...@goldstag.com* (Melvin C.
> Etheridge) wrote:
> >How can I mirror www.xyz.com to two servers?
> >
> >Say if one server goes down the other one will answer back.
>

> Cisco's LocalDirector product, from what little I know about it, might
> help address this. It can return a list of IP addresses with the
> entries sorted according to some notion of "load" on the target, which
> one would hope also accounts for the target being down.
>

Not to sound too much like a commercial, but another option is to have
a look at our "Big/IP", which has the fault tolerant features you seem to
be looking for. Have a look at www.f5.com, for some white paper like
specs.

m.

Matt Sommer, Network Systems Engineer InterNIC: MMS26
F5 Labs, Inc. 1218 3rd Ave., Suite 508 Seattle, WA 98101
e-mail: m...@f5.com Voice: 206.447.1817 Fax: 206.447.9636
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